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Joaquin Phoenix‘s much-publicized retirement from acting in order to pursue his burgeoning career as a rapper had cries of “Hoax!” surrounding it from the very beginning, and its subsequent critical and audience response was mostly negative. However, despite the apparent trend of people upset at being duped, Casey Affleck’s I’m Still Hereis a fascinating and frequently hilarious send-up of celebrity culture anchored by an amazingly committed performance from Phoenix. In the film, as in reality, this is the kind of thing that could potentially end a career and forever ruin a reputation, and the courage he displays in sticking to it is very impressive.

In one of the best scenes, Phoenix rejects an offer to co-star with Ben Stiller (who you would never guess by watching is in on the joke the whole time) in Greenberg; in another, he hilariously attempts to obtain a record deal with Sean “Puffy” Combs, who isn’t quite the actor Stiller is, though his performance is just good enough that its weaker elements could be seen as arrogant posturing for the cameras that follow Phoenix everywhere. Then there is the famous David Letterman interview, in which he mumbles and stares blankly at the roaring audience, seemingly unable to fathom why they think he’s so funny (Letterman was not in on the joke, but of course he is unfazed after previous encounters with the likes of Crispin Glover and Harmony Korine).

So, what of the supposed rapping, you ask? Is it any good? The answer is a resounding “not really.” While the filmmakers wisely make it just decent enough to convince us that an arrogant movie star who has lost his mind to drugs and the excess of stardom would believe it was his new calling, his flows are about what you’d see in the mid-range of a good Hip-Hop open mic. The rhymes are clumsy and mostly monosyllabic, the beats generic; Phoenix’s delivery is full of the gruff showmanship of a spoiled rich dude with no real inkling of the dues a great emcee must pay. The funniest part about it is that at his few live appearances as a rapper, star-struck morons who are clearly just tickled to be near an Oscar-nominated actor mostly cheer him on. At one such performance he tells the lone heckler, “I’ve got a million dollars in my bank account – what do you got?” Cue the cheers.

This is why the film works, and why it is has not permanently damaged Phoenix’s acting career. By committing himself so fully to the performance and taking a great risk of being reviled and blacklisted by the Hollywood community, Phoenix has made a strong and convincing statement about our celebrity culture and the idea of reinventing oneself. Beyond any of that, though, it’s a very fun movie to watch, and all the more impressive for making you wonder what’s real even when you know it’s a hoax.

Chris Willman offers some interesting observations about Phoenix and the rumored hoax.

What to make, then, of the grainy video footage of this erstwhile perfectionist stumbling around on stage in Las Vegas, kicking off his supposed new career as a rapper? Of the announcement that he was retiring from movies to achieve new levels of excellence in his true calling, hip-hop? The documentary cameras tracking his every suddenly awkward move? Even if Phoenix never previously seemed like Mr. Levity, it seemed easy enough — to me, anyway — to write off his intentions to be the new Eminem (or Everlast) as a very elaborate gag. But after his appearance as a heavily bearded, disheveled catatonic on Letterman Wednesday night, which ended with the host invoking Farrah Fawcett as a comparatively more lucid guest, the stakes suddenly got higher. Columnists and bloggers predicted the end of Phoenix’s career, even if he should abandon hippity-hop and come crawling back to movies. Fans and detractors lamented his transformation from the potential Brando of his generation into the poster child for “just say no” (to drugs, Vanilla Ice, or both). Half the viewers thought the standoff with Dave was hilarious, and half deeply sad, but in either case, most figured the laughs or tears were on Phoenix.

Which makes this potentially one of the greatest performances any modern actor has ever given — or at least one of the most baldly courageous. The closest comparison would have to be Andy Kaufman’s utter commitment to his obnoxious Tony Clifton persona, but Phoenix is going Kaufman one braver here, by not slapping a fake name on the alter ego bur rather inviting the audience to mistake his damaged doppelganger for himself, over an indeterminate length of time that could leave his “real” career hanging in limbo. There is an end in sight: Phoenix’s pal Casey Affleck is shooting all this for what insiders presume is a mockumentary about the breakdown of a burned-out actor. The risk, of course, is how lame it might turn out to be if Phoenix and Affleck remove the masks and say “just kidding” when it’s time for their film to finally come out. My hunch is that if they’re taking it this far — and watching Letterman, it was clear that Phoenix is in deep, deep, deep cover — they might take it all the way into and past the premiere and continue insisting that Phoenix’s actorly dissolution was legit.